That chart is probably overly dramatic (and they conveniently sell tranny coolers), but the fundamentals seems true that you don't want the ATF going beyond about 225°F.
The thermal expansion coefficient of materials is constant, most aluminums being about 12 to 13 ppm (e.g. microinch) per °F and irons are typically about 6 to 7. My main worry would be ruining the fluid more than the marginally worse metal expansion. Joining dissimilar metals is a bad idea but unfortunately common on our junk.
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Last edited by DaveInDenver; 05-31-2013 at 07:06 PM.